This invention relates to pitch-free graphite articles and to a process for making the same without using a conventional binder such as pitch as is employed in the prior art.
Most graphite articles require a pitch binder phase to cement carbon particles together since carbon does not melt or form liquid phases at moderate temperatures and pressures. The process is complicated, costly, and time consuming.
When a pitch binder is used, gases from volatile matter are produced and escape from the carbon solid by the decomposition of the pitch binder phase during baking to form carbon, leaving some voids or pores in it. Therefore, in order to make a high-density, strong, carbon, techniques have been used such as repeated impregnation with pitch and heat-treatment in an autoclave, use of high yield pitches or filling up pores with a decomposition of pyrolytic carbon. Even by these treatments, it is difficult to obtain dense graphite solids with low permeability.
The demand for development of new advanced carbon materials has been increasing in various scientific fields to support recent advanced technology, especially development of strong and dense graphite materials which can be used in various new fields such as aerospace, biomaterials, nuclear applications, mechanical seals, crucibles, and high temperature machine parts.
Graphite products are currently produced by the complicated and lengthy process described below:
______________________________________ 1. HOT MIXING: Carbonaceous material, usually calcined coke, is hot mixed with pitch to coat the coke particles with pitch. 2. FORMING: The hot mixes are either extruded or molded into shapes. 3. BAKING: Formed shapes are baked very slowly, 5.degree. C./hr, to about 850.degree. C. to decompose the pitch and convert it to coke. 4. IMPREGNATION Baked shapes are impregnated REBAKE: with pitch type materials to increase density followed by rebaking; frequently more than one cycle is needed. 5. GRAPHITIZATION: Baked shapes are reheated to 2800.degree. C. to thermally rearrange the carbonaceous material into a crystalline form having an ordered pattern of stacked parallel planes characteristic of graphite. This is accompanied by a desirable change in the physical properties. ______________________________________